DE102021114295A1 - METHOD AND APPARATUS FOR DETERMINING AN INTENSITY VALUE REPRESENTING AN INTENSITY OF LIGHT REFLECTED BY AN OBJECT IN A SCENE - Google Patents

Abstract

A method of determining an intensity value that represents an intensity of light reflected from an object in a scene. The method includes performing a time-of-flight (ToF) measurement of the scene using a ToF sensor. A light-intensity-independent correlation function of a photosensitive pixel of the ToF sensor has a plateau in a target measurement range for the ToF measurement. The object is within the target measurement area. The method further includes determining the intensity value based on an output of the photosensitive pixel for the ToF measurement.

Description

Area

The present disclosure relates to intensity detection of time-of-flight (ToF) sensors. In particular, examples relate to a method and apparatus for determining an intensity value representing an intensity of light reflected from an object in a scene.

background

A traditional ToF camera measures distance by emitting near-infrared light. In various applications, such as face recognition, detailed depth is not the primary measurement objective. More important is a grayscale image that shows the amount of light reflected. This image can be created, for example, by integrating the received light into one of the charge containers. The number of electrons in the container is a direct indication of the amount of light reflected. In other approaches, the grayscale image is generated based on an amplitude of the measured correlation. Semi-transparent objects obscuring the imager introduce reflections that are undesirable in the measurement.

Thus, there is a need for improved intensity detection using ToF sensors.

summary

The need may be met by the subject matter of the appended claims.

One example relates to a method of determining an intensity value representing an intensity of light reflected from an object in a scene. The method includes performing a ToF measurement of the scene using a ToF sensor. A light-intensity-independent correlation function of a photosensitive pixel of the ToF sensor has a plateau in a target measurement range for the ToF measurement. The object is within the target measurement area. The method further includes determining the intensity value based on an output of the photosensitive pixel for the ToF measurement.

Another example relates to an apparatus for determining an intensity value representing an intensity of light reflected from an object in a scene. The device includes a ToF sensor that is designed to carry out a ToF measurement of the scene. A light-intensity-independent correlation function of a photosensitive pixel of the ToF sensor has a plateau in a target measurement range for the ToF measurement. The object is within the target measurement area. The device additionally includes a processing circuit that is designed to determine the intensity value based on the output of the photosensitive pixel for the ToF measurement.

character list

• 1 zeigt ein Flussdiagramm eines Beispiels eines Verfahrens zum Bestimmen eines Intensitätswertes;
• 2 zeigt ein Beispiel einer Vorrichtung zum Bestimmen eines Intensitätswertes;
• 3 zeigt eine beispielhafte Korrelationsfunktion;
• 4 zeigt eine beispielhafte Beziehung zwischen Plateaubegrenzungen und einem Tastgrad von moduliertem Licht;
• 5A bis 5E zeigen eine beispielhafte Beziehung zwischen einer Korrelationsfunktion und einer Zeitverschiebung zwischen moduliertem Licht und einem Referenzsignal; und
• 6 zeigt eine weitere beispielhafte Korrelationsfunktion.

Some examples of devices and/or methods are described below solely by way of example and with reference to the accompanying figures, in which the following applies:

• 1 shows a flowchart of an example of a method for determining an intensity value;
• 2 shows an example of a device for determining an intensity value;
• 3 shows an example correlation function;
• 4 Figure 12 shows an exemplary relationship between plateau limits and a duty cycle of modulated light;
• 5A until 5E show an exemplary relationship between a correlation function and a time shift between modulated light and a reference signal; and
• 6 shows another exemplary correlation function.

Detailed description

Some examples will now be described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these exemplary embodiments described in detail. Other examples may include modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe particular examples is not intended to be limiting of other possible examples.

Throughout the description of the figures, the same or similar reference numbers refer to the same or similar elements and/or features, which may be identical or implemented in modified form while providing the same or similar function. Also, in the figures, the thicknesses of lines, layers, and/or areas may be exaggerated for clarity.

When two elements A and B are combined using an “or”, it is to be understood that all possible combinations are disclosed, ie only A, only B, and A and B, unless expressly defined otherwise in a particular case. As an alternative wording for the same combinations, "at least one of A and B" or "A and/or B" can be used. The same applies to combinations of more than two elements.

If a singular form, e.g. For example, when "a, an" and "the" are used and use of only a single element is not explicitly or implicitly required, other examples may use multiple elements to implement the same function. Where a function is described below as being implemented using multiple elements, other examples may implement the same function using a single element or processing entity. It is further understood that the terms "comprises," "comprising," "has," and/or "comprising" when used mean the presence of the specified features, integers, steps, operations, processes, elements, components, and/or a group thereof describe without excluding the presence or addition of any other feature, integer, step, operation, process, element, component and/or group thereof.

1 FIG. 10 shows a flow chart of an example of a method 100 for determining an intensity value representing an intensity of light reflected from an object in a scene. The method 100 is further described below with reference to FIG 2 which shows an example apparatus 200 for determining an intensity value representing an intensity of light reflected from an object 201 in a scene.

The device 200 includes a ToF sensor 210. The ToF sensor 200 includes an illumination element (circuitry, component) 230 for emitting modulated light 202 to a scene comprising the object 201 and a light-sensing element (circuitry, component) 220 for detecting the of of the scene received light 203.

The lighting element 230 generates the modulated light 202. The lighting element 230 may include any number of light sources. The lighting element 230 can e.g. B. one or more light-emitting diodes (LEDs; Light-Emitting Diodes) and/or one or more laser diodes (e.g. one or more surface-emitting diode lasers (VCSELs, Vertical-Cavity Surface-Emitting Lasers). Lighting signal are ignited.

The light sensing element 220 may include various components, such as. optics (e.g. one or more lenses) and electronic circuitry. In particular, the electronic circuit arrangement comprises an image sensor with at least one photosensitive element or pixel (e.g. with a photonic mixer device, PMD (photomixing detector), or a charge-coupled device, CCD (charge-coupled device). The image sensor can, for example, have a plurality of photosensitive elements or pixels The at least one photosensitive element or pixel is driven based on a reference signal.

The method 100 includes performing 102 a ToF measurement of the scene using the ToF sensor 210. The lighting element 230 emits the modulated light 202 to the scene during the ToF measurement. Furthermore, the at least one photosensitive element or pixel is controlled based on the reference signal during the ToF measurement. The reference signal has an alternating series of high and low pulses of equal duration. Analogously, the modulated light 202 has a sequence of light pulses with the same pulse length (duration) and the same pulse spacing. In other words, a continuous wave (CW) ToF measurement is performed.

The parameters of the ToF sensor 210 are set such that a (light intensity-independent) correlation function of the at least one photosensitive pixel of the ToF sensor 210 has a plateau (i.e. a substantially constant value) in a target measurement range for the ToF measurement. The (light-intensity-independent) correlation function gives the distance-dependent correlation of the received light 203 of the photosensitive pixel with the reference signal, and without considering (i.e. ignoring, not considering) the intensity of the light 203 . In other words, the (light intensity independent) correlation function only describes the distance dependence of the photosensitive pixel output (i.e. the dependence of the photosensitive pixel output on the distance between the ToF sensor 210 and the object 201), but not the dependence of the photosensitive pixel output on the intensity of the received light 203. If the ToF sensor 210 has a plurality of photosensitive pixels, the respective (light intensity-independent) correlation function of each photosensitive pixel can be adjusted as described above.

3 shows an exemplary (light intensity-independent) correlation function 310. The abscissa in 3 indicates the distance between the ToF sensor 210 and the object 201. The ordinate indicates the value of the correlation function 310. Furthermore, the distance values "Dist-min" and "Dist-max" denote the limits of an exemplary target measuring range 320 of the ToF sensor 210. The object 201 is located within the target measuring range 320.

How out 3 As can be seen, the correlation function 310 has a plateau in the target measurement range 320 . In other words, the correlation function 310 is "flat" in the target measurement range 320 and therefore has essentially the same value in the target measurement range 320 .

Due to the constant value of the correlation function 310 in the target measurement area 320, the ToF measurement is not sensitive to the distance between the ToF sensor 210 and the object 201 in the target measurement area 320.

The (actual) output of the photosensitive pixel of the ToF sensor 210 for the ToF measurement scales with the intensity (i.e. the luminous intensity) of the light 203 reflected from the object 201. For example, the output of the photosensitive pixel of the ToF sensor 210 for the ToF measurement can be determined by the product of the intensity of the received light 203 during the ToF measurement and the value of the (light intensity-independent) correlation function in the distance of the object 201 causing the received reflections. Accordingly, the output (value) of the photosensitive pixel of the ToF sensor 210 scales with the intensity of the light 203 reflected from the object 201, in the event that the object 201 is within the target measurement area 320, but not with the distance between the ToF -sensor 210 and the object 201. In other words, the output (value) of the photosensitive pixel of the ToF sensor 210 is proportional to the intensity of the light 203 reflected by the object 201 - independent of the distance between the ToF sensor 210 and the Object 201. Therefore, the output (value) of the photosensitive pixel of the ToF sensor 210 allows characterizing the intensity of the light 203 reflected from the object 201 using a correlation function for the ToF measurement as described above.

Referring again to 1 the method 100 further includes determining 104 an intensity value based on the output of the photosensitive pixel for the ToF measurement. The intensity value represents the intensity of the light 203 reflected from the object 201 in the scene. For example, determining 104 the intensity value may include applying at least one correction to the output (value) of the photosensitive pixel of the ToF sensor 210 for the ToF measurement . The output (value) of the photosensitive pixel of the ToF sensor 210 can be e.g. B. be scaled and / or offset-corrected to get the intensity value. Accordingly, various errors (e.g. noise) can be corrected.

The device 200 includes a correspondingly designed processing circuit 240 which is coupled to the ToF sensor 210 . The processing circuitry 240 may e.g. B. a single dedicated processor, a single shared processor, or a plurality of individual processors, some or all of which may be shared, digital signal processor (DSP) hardware, an application specific integrated circuit (ASIC). integrated circuit) or a field programmable gate array (FPGA; field programmable gate array). Processing circuitry 240 may optionally be coupled, for example, to read only memory (ROM) for storing software, random access memory (RAM), and/or non-volatile memory. The processing circuit 240 is configured to determine the intensity value, which indicates the intensity of the light 203 reflected by the object 201, based on the output (value) of the photosensitive pixel of the ToF sensor 210 for the ToF measurement.

Although the processing circuit 240 in the example of FIG 2 shown as a separate element, processing circuitry 240 may be integrated into ToF sensor 210 in alternative examples.

The processing circuitry 240 may also output data indicative of the intensity value. For example, the processing circuitry 240 may be configured to generate a grayscale image of the scene including the pixel representing the determined intensity value. The method 100 can include a corresponding method step. If a plurality of the photosensitive pixels are used, the grayscale image of the scene may include a plurality of pixels each representing the particular intensity value of a respective one of the photosensitive pixels of the ToF sensor 210 . The output data of the processing circuit 240 can be used for various applications such as e.g. B. face recognition can be used.

Device 200 may also include other hardware, conventional and/or custom.

In other words, a method and an apparatus for detecting the amount of light reflected from the object 201, which requires only a single measurement with the ToF sensor 210, is proposed. In contrast to conventional approaches, the proposed method does not require depth measurements to obtain the intensity information. For example, the proposed method may allow grayscale images to be acquired more frequently than with conventional approaches, since it is not necessary to obtain four different raw images. The grayscale image does not require precise "wiggle" calibration and is therefore free from systematic sources of error that are difficult to calibrate.

The target measurement range of the ToF sensor 210 depends on the modulation frequency used for the ToF measurement. In particular, the modulation frequency denotes the modulation frequency of the reference signal used to drive the photosensitive pixel of the ToF sensor 210 and the modulated light 202 emitted into the scene during the ToF measurement. The target measurement range is within the clear distance range d _u as in 3 shown. The maximum, unambiguous distance range d _u of the ToF measurement is inversely proportional to the modulation frequency ƒ _mod : $${\mathrm{i.e}}_{\mathrm{and}}=\frac{c}{2\cdot {ƒ}_{mO\mathrm{i.e}}}$$

Objects measured beyond this distance will wrap around to fall in the range [0,d _u ], appearing to be much closer than they actually are. The unambiguous distance range d _u of the ToF measurement determines the signal range d _sr for which a non-zero output of the photosensitive pixel of the ToF sensor 210 is produced: $${\mathrm{i.e}}_{s\mathrm{right}}=\frac{{\mathrm{i.e}}_{\mathrm{and}}}{2}$$

The target measurement range of the ToF sensor 210 is the distance range for which valid intensity measurements are obtained, i. H. the plateau of the correlation function. The duty cycle of the modulated light 202 affects the range of distances in which the correlation increases to the plateau.

The duty cycle of a signal is the fraction of a period that the signal is active. The duty cycle of the modulated light 203 indicates the ratio of the summed durations of the light pulses to the total period (duration) of the modulated light 202, for example. Similarly, the duty cycle of the reference signal used to drive the photosensitive pixel of the ToF sensor 210 denotes the ratio of the summed durations of the high pulses (or alternatively the low pulses) to the total period (duration) of the reference signal.

Similarly, the duty cycle of the modulated light 202 affects the range of distances over which the correlation falls off the plateau. Since this correlation is symmetric, the distance range d _min , in which the correlation increases towards the plateau, can be subtracted twice from the signal range d _sr to get the length of the target measurement range d _mr : $${\mathrm{i.e}}_{m\mathrm{right}}={\mathrm{i.e}}_{s\mathrm{right}}-2\cdot {\mathrm{i.e}}_{min}$$

The distance range dmin is determined by the duty cycle DC. Assuming that the duty cycle is defined between 0 and 1 (i.e. a whole period is considered), the distance range dmin can be defined as follows: $${\mathrm{i.e}}_{min}=\frac{DC\cdot {\mathrm{i.e}}_{\mathrm{and}}}{2}$$

Combining the above mathematical expressions, the length of the target measurement area d _mr can be expressed as: $${\mathrm{i.e}}_{m\mathrm{right}}={\mathrm{i.e}}_{\mathrm{and}}\cdot \left(0.5-DC\right)$$

Accordingly, the target measurement range of the ToF sensor 210 is from dmin to dmin + d _mr .

As can be seen from the mathematical expression (5), the length of the target measurement range d _mr is inversely proportional to the duty cycle DC. The lower the duty cycle DC, the greater the length of the target measuring range d _mr . Furthermore, from mathematical expression (5), the duty cycle of the modulated light 202 emitted into the scene should be less than 0.5 in order to obtain a correlation function that has a plateau.

4 Fig. 12 schematically shows the relationship between the plateau boundaries and the duty cycle of the emitted modulated light. 4 shows an exemplary (light-intensity-independent) correlation function 410, which has the same form (the same course) as that in FIG 3 correlation function 310 shown. The ordinate of 4 gives the value of the correlation function 410. The abscissa of 4 indicates the time shift between the light received from the object 201 and the reference signal 430 used to drive the photosensitive pixel of the ToF sensor 210. The time shift corresponds to (is proportional to) the distance between the ToF sensor 210 and the object 201. The light that the photosensitive pixel of the ToF sensor 210 from the object 201 receives, is in 4 represented by a reflection 420 of the originally emitted modulated light. Like the modulated light 202 emitted into the scene, the received reflection 420 comprises a plurality of light pulses 421, 422, .... The pulse length (duration) and pulse spacing of the light pulses of the received reflection 420 is essentially identical to that Pulse length and the pulse spacing of the light pulses of the emitted modulated light 202.

As shown for the light pulse 421, the pulse length of the light pulse 421 determines the distance range d _min . Similarly, the pulse length of the light pulse 422 determines the range of distances over which the correlation falls from the plateau. The pulse length of the light pulses of the received reflection 420, ie effectively the pulse length of the emitted light 202, is determined by the duty cycle of the emitted light 202. Therefore, the position target measurement range is adjustable by the duty of the emitted light 202 . For example, the duty cycle of the modulated light 202 may be equal to or less than 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, or 0.1. The duty cycle of the modulated light 202 is less than the duty cycle of the reference signal.

The effect of the duty cycle of the modulated light 202 on the target measurement area is due to the internal charge separation of the photosensitive pixel of the ToF sensor 210 . As described above, the photosensitive pixel of the ToF sensor 210 is driven based on the reference signal. Depending on a signal value of the reference signal, the photosensitive pixel selectively stores charges that are generated in the photosensitive pixel during the ToF measurement in one of two charge storage devices of the photosensitive pixel. The charge stores of the photosensitive pixel can be capacitors or potential wells, for example, which are formed in a semiconductor material of the photosensitive pixel. this is in 4 illustrated using the exemplary reference signal 430 .

When the reference signal 430 is high, e.g. B. while the reference signal 430 has the high pulse 431, the photosensitive pixel of the ToF sensor 210 stores charges, which are generated by the received light 203 in the semiconductor material of the photosensitive pixel, in the first of the two charge stores. This is indicated by the letter "A" in 4 displayed, which designates the first charge storage device. When the reference signal 430 is low, the photosensitive pixel of the ToF sensor 210 stores charges, which are generated by the received light 203 in the semiconductor material of the photosensitive pixel, in the second of the two charge storage devices. This is indicated by the letter "B" in 4 displayed, which designates the second charge storage device.

In the example of 4 is the time shift between the received reflection 420 and the reference signal 430 (i.e. the distance between the ToF sensor 210 and the object 201) such that approximately half of the charges generated in the semiconductor material of the photosensitive pixel by the respective light pulse 421, 422 in each of the two charge stores goes. Consequently, the correlation is zero. The value of the correlation function depends on the time shift between the received reflection 420 and the reference signal 430 and thus on the distance between the ToF sensor 210 and the object 201 .

This is also in 5A until 5E 10, which show the relationship between the value of the correlation function and the time shift between the received light and the reference signal used to drive the photosensitive pixel of the ToF sensor 210. The ordinate in each of the 5A until 5E denotes the value of the correlation function. The abscissa in each of the 5A until 5E indicates the time shift between the light received from the object 201 and the reference signal 530 used to drive the photosensitive pixel of the ToF sensor 210. The time shift corresponds to (is proportional to) the distance between the ToF sensor 210 and the object 201. The light that the photosensitive pixel of the ToF sensor 210 receives from the object 201 is reflected in 5A until 5E represented by a reflection 520 of the originally emitted modulated light.

Analogous to the example of 4 For example, the photosensitive pixel of the ToF sensor 210 stores charges generated in a semiconductor material of the photosensitive pixel by the reflection 520 (ie the received light) in the first of the two charge stores when the reference signal 530 is high, e.g. B. while the reference signal 530 has the high pulse 531. This is in turn indicated by the letter "A" in 5 displayed, which designates the first charge storage device. When the reference signal 530 is low, the photosensitive pixel of the ToF sensor 210 stores charges generated in the semiconductor material of the photosensitive pixel by the reflection 520 (ie the received light) in the second of the two charge stores. This is indicated by the letter "B" in 5 displayed, which designates the second charge storage device.

In 5A the object 201 is located outside the target measurement area. Accordingly, the time difference between the received Reflection 520 and the reference signal 530 such that the light pulse 521 (the reflection 520) in the semiconductor material of the photosensitive pixel charges generated in the second of the two charge storage, ie the charge storage B, are stored.

In 5B the distance of the object 201 to the ToF sensor 210 is increased, but the object 201 is not yet in the target measurement area. Analogous to the example of 4 the time shift between the received reflection 520 and the reference signal 430 is such that approximately half of the charges generated in the semiconductor material of the photosensitive pixel by the light pulse 521 go into each of the two charge stores. Consequently, the correlation is zero. Correlation function 510 increases as more and more of the generated charges are stored in charge storage A .

Since the correlation is essentially zero at this specific distance, an element covering the ToF sensor 210 can be placed at this distance with respect to the ToF sensor 210 . For example, a cover glass or a display covering the ToF sensor 210 can be placed at this distance such that reflections of the emitted light 202 from this element do not affect the ToF measurement. In general, an element covering the ToF sensor 210 can be placed at any predetermined distance with respect to the ToF sensor 210 for which an absolute value of the (light intensity independent) correlation function is less than 10%, 5% or 1% of a absolute value of the (light intensity independent) correlation function at the plateau. For example, the placement of a display covering the ToF sensor 210 at a distance for which the correlation is essentially zero is further in the left part of FIG 3 shown.

Furthermore, it should be noted that the above discussion is not limited to elements covering the ToF sensor 210 . In general, the (light intensity independent) correlation function can be designed such that an absolute value of the light intensity independent correlation function at any predetermined (target, desired) distance is less than 10%, 5% 10% of an absolute value of the light intensity independent correlation function on the plateau. For example, if there is another unwanted (interfering) object in the scene at a certain distance with respect to the ToF sensor 210, the (light intensity independent) correlation function can be designed such that an absolute value of the light intensity independent correlation function at that distance is less than 10%. , 5% or 1% of an absolute value of the light intensity independent correlation function on the plateau. Accordingly, reflections of the emitted light received from the undesired object practically do not affect the ToF measurement for the object 201 .

As described above, the amount of charge stored in the charge storage device A increases as the distance between the object 201 and the ToF sensor 210 increases. The distance from which all generated charges are stored in the charge store A designates one of the limitations of the plateau of the correlation function 510 and thus one of the limitations of the target measurement range. this is in 5C shown. In 5C charges are no longer stored in charge storage device B, but are only stored in charge storage device A. The smaller the light pulse 521, ie the smaller the duty cycle of the emitted modulated light 202, the smaller the distance from which all the generated charges are stored in the charge store A.

As long as the object 201 is in the target measurement region, the charges generated by the light pulse 521 are stored in the charge store A. The length of the plateau of the correlation function 510 and thus of the target measurement region is determined by the modulation frequency of the emitted modulated light 203 and the reference signal 530 . The lower the modulation frequency, the longer the length of the plateau of the correlation function 510. This is in 5D shown.

The distance from which the generated charges are no longer only stored in the charge store A designates the other limitation of the plateau of the correlation function 510 and thus the other limitation of the target measurement range. this is in 5E shown. The distance of the object 201 from the ToF sensor 210 is further increased in such a way that the object 201 leaves the target measurement area. Accordingly, more and more of the generated charges are stored in charge storage B and fewer charges in charge storage A, such that the correlation function falls from the plateau. In the example of 5E the time shift between the received reflection 520 and the reference signal 430 is such that approximately half of the charges generated in the semiconductor material of the photosensitive pixel by the light pulse 521 go into each of the two charge stores. Consequently, the correlation is zero. For example, the distance for which the correlation function 510 is again zero can be chosen such that the influence of reflections received from an undesired (interfering) object located in the scene at this distance on the ToF measurement is minimized.

In order to obtain the output (value) of the photosensitive pixel of the ToF sensor 210, different readout approaches are possible. For example, the output of the photosensitive pixel for the ToF measurement can only be based on (determined by) the charges that are accumulated in one of the two charge stores during the ToF measurement. The output (value) of the photosensitive pixel for the ToF measurement can e.g. B. based only on the charges stored in the charge storage device A, but not on the charges stored in the charge storage device B in the examples of FIG 4 and 5A until 5E . In alternative examples, the output (value) of the photosensitive pixel for the ToF measurement may be based on (determined by) a difference between the charges accumulated in the two charge reservoirs during the ToF measurement. The output (value) of the photosensitive pixel for the ToF measurement can e.g. B. on the amount of charge C A stored in charge storage _A minus the amount of charge C B stored in charge storage _B in the examples of FIG 4 and 5A until 5E based. By basing the output (value) of the photosensitive pixel for the ToF measurement on the difference between the charges accumulated in the two charge reservoirs, it can be possible to reduce the background light effects and thus the accuracy of the output (value) of the photosensitive improve pixels.

In summary, a single measurement with a rather atypical CW modulation is proposed. As described above, the position of the correlation can be tuned such that the zero crossing is at the position of interfering objects such as a display or a coverslip. The duty cycle is tuned to produce the plateau of the correlation function. The measuring range is within the plateau. Since the correlation is constant on the plateau, the values obtained correspond to the received signal strength, which is the same as for grayscale images. The minimum distance (Dist-min in 3 ) and the maximum distance (Dist-max in 3 ) that define the plateau are both dependent on the modulation frequency used. In the area of the plateau, an intensity measurement is possible.

In order to eliminate systematic measurement errors, an additional ToF measurement can be carried out. The reference signal used to drive the photosensitive pixel of the ToF sensor 210 in the other ToF measurement is inverted with respect to the reference signal used to drive the photosensitive pixel in the (first) ToF measurement (described above). . In other words, the reference signal for the further ToF measurement is 180° out of phase with the reference signal for the original ToF measurement. Accordingly, the intensity value can be determined based on the difference between the output (value) of the photosensitive pixel of the ToF sensor 210 for the ToF measurement and the output (value) of the photosensitive pixel of the ToF sensor 210 for the further ToF measurement.

The target measurement range can be determined at runtime using the ToF sensor. For example, one or more additional ToF measurements may be performed using ToF sensor 210 . A distance value indicative of the distance of the ToF sensor 210 to the object 201 may be determined based on the output (value(s)) of the ToF sensor for the one or more further ToF measurements. The distance value may be calculated according to conventional ToF - Depth sensing principles can be determined based on the output (value(s)) of the ToF sensor for the one or more further ToF measurements Accordingly, the target measurement range can be determined based on the distance value such that the object 201 is within the target measurement range .

Optionally, based on the output (value(s)) of the ToF sensor for the one or more further ToF measurements, it can be determined whether further objects (i.e. objects in addition to the object 201) are present in the scene. If it is determined that further objects are present in the scene, the parameters of the ToF sensor 210 can be set in such a way that a respective absolute value of the (light intensity-independent) correlation function is less than 10% at the respective distance of the one or more further objects. of an absolute value of the (light intensity independent) correlation function at the plateau.

If the object 201 is further away from the ToF sensor, the (light intensity independent) correlation function can be made to include one or more more plateaus instead of lengthening the first plateau by lowering the modulation frequency. this is in 6 shown as an example. 6 shows an exemplary (light intensity-independent) correlation function 610. The abscissa in 6 indicates the distance between the ToF sensor 210 and the object 201. The ordinate indicates the value of the correlation function 610.

Correlation function 610 has a first plateau 611, similar to correlation functions 310 and 410 in FIG 3 and 4 . The first plan teau 611 corresponds to a first target measurement area for the ToF measurement. In addition, the correlation function 610 has a second plateau 612, which corresponds to a second target measurement range for the ToF measurement.

Optionally, the correlation function 610 can include further plateaus corresponding to further target measurement ranges for the ToF measurement. In general, a (light intensity-independent) correlation function according to the present disclosure can have at least one further plateau in at least one further target measurement range for the ToF measurement.

If the object is in a target measurement area that corresponds to a plateau with a negative value, the output (value) of the photosensitive pixel of the ToF sensor 210 can be corrected (eg, multiplied by -1) to obtain the intensity value.

As in 6 is displayed, the zero crossings of the correlation function 610 can be chosen such that they are at distances from interfering objects, such as e.g. B. a display that covers the ToF sensor 210 lie.

In other examples, multiple ToF measurements may be performed to cover multiple target measurement ranges. For example, a ToF measurement may be performed as described above to obtain an output (value) of the photosensitive pixel of the ToF sensor 210 for a first target measurement area. In addition, another ToF measurement of the scene can be performed using the ToF sensor. The (light-intensity-independent) correlation function of the photosensitive pixel has a plateau in a further, second target measurement range for the other ToF measurement. The (light intensity-independent) correlation function for the first ToF measurement can e.g. B. only the in 6 include the illustrated plateau 611 and the other (light intensity-independent) correlation function for the second ToF measurement can e.g. B. only the in 6 plateau 612 shown. Accordingly, two target measurement ranges can be covered with two ToF measurements.

The intensity value can be determined based on the output (value) of the photosensitive pixel for the ToF measurement and the output (value) of the photosensitive pixel for the other ToF measurement. For example, the outputs (output values) for both ToF measurements can be added and optionally scaled to get the intensity value.

Optionally, further ToF measurements with (light intensity-independent) correlation functions, which have a corresponding plateau in further target measurement areas, can be used.

• Einige Beispiele betreffen ein Verfahren zum Bestimmen eines Intensitätswertes, der eine Intensität von Licht, das von einem Objekt in einer Szene reflektiert wird, darstellt. Das Verfahren umfasst ein Durchführen einer ToF-Messung der Szene unter Verwendung eines ToF-Sensors. Eine lichtintensitätsunabhängige Korrelationsfunktion eines photosensitiven Pixels des ToF-Sensors weist ein Plateau in einem Zielmessbereich für die ToF-Messung auf. Das Objekt befindet sich innerhalb des Zielmessbereichs. Das Verfahren umfasst ferner ein Bestimmen des Intensitätswertes basierend auf einer Ausgabe des photosensitiven Pixels für die ToF-Messung.

The examples as described herein can be summarized as follows:

• Some examples relate to a method for determining an intensity value representing an intensity of light reflected from an object in a scene. The method includes performing a ToF measurement of the scene using a ToF sensor. A light-intensity-independent correlation function of a photosensitive pixel of the ToF sensor has a plateau in a target measurement range for the ToF measurement. The object is within the target measurement area. The method further includes determining the intensity value based on an output of the photosensitive pixel for the ToF measurement.

In some examples, the light-intensity-independent correlation function indicates the distance-dependent correlation of the light of the photosensitive pixel with a reference signal and without considering the intensity of the light, where the photosensitive pixel is driven based on the reference signal.

According to some examples, determining the intensity value includes applying at least one correction to the output of the photosensitive pixel for the ToF measurement.

In some examples, performing the ToF measurement includes: illuminating the scene with modulated light; and driving the photosensitive pixel based on a reference signal, the reference signal comprising an alternating train of high and low pulses of equal duration, and the modulated light comprising a train of light pulses of equal pulse length and equal pulse spacing.

According to some examples, a duty cycle of the modulated light is less than a duty cycle of the reference signal.

In some examples, the method further comprises performing a further ToF measurement, wherein the reference signal used to drive the photosensitive pixel in the further ToF measurement is related to the reference signal used to drive the photosensitive pixel in the ToF measurement is used, is inverted, and the intensity value is based on a difference between the output of the photosensitive pixel for the ToF measurement and an output of the photosensitive pixel for further ToF measurement.

According to some examples, depending on a signal value of the reference signal, the photosensitive pixel selectively stores charges generated in the photosensitive pixel during the ToF measurement in one of two charge storage devices of the photosensitive pixel, and the output of the photosensitive pixel is used for the ToF Measurement based only on the charges accumulated in one of the two charge stores during the ToF measurement.

In alternative examples, depending on a signal value of the reference signal, the photosensitive pixel selectively stores charges generated in the photosensitive pixel during the ToF measurement in one of two charge storage devices of the photosensitive pixel, and the output of the photosensitive pixel is used for the ToF Measurement based on a difference between the charges accumulated in the two charge stores during the ToF measurement.

In some examples, the light intensity independent correlation function has at least one further plateau in at least one further target measurement range for the ToF measurement.

According to some examples, the method further comprises: performing another ToF measurement of the scene using the ToF sensor, wherein the light intensity independent correlation function of the photosensitive pixel for the further ToF measurement has a plateau in another target measurement area; and determining the intensity value based on the output of the photosensitive pixel for the ToF measurement and an output of the photosensitive pixel for the other ToF measurement.

In some examples, an absolute value of the light intensity independent correlation function at a predetermined distance is less than 10% of an absolute value of the light intensity independent correlation function at the plateau.

According to some examples, an element covering the ToF sensor is arranged at the predetermined distance with respect to the ToF sensor.

In some examples, the method further includes: performing one or more further ToF measurements using the ToF sensor; determining a distance value indicative of a distance to the object based on an output of the ToF sensor for the one or more further ToF measurements; and determining the target measurement area based on the distance value.

According to some examples, the method further includes generating a grayscale image of the scene including the pixel representing the determined intensity value.

Other examples relate to an apparatus for determining an intensity value representing an intensity of light reflected from an object in a scene. The device includes a ToF sensor that is designed to carry out a ToF measurement of the scene. A light-intensity-independent correlation function of a photosensitive pixel of the ToF sensor has a plateau in a target measurement range for the ToF measurement. The object is within the target measurement area. The device additionally includes a processing circuit that is designed to determine the intensity value based on the output of the photosensitive pixel for the ToF measurement.

Examples of the present disclosure may enable ToF grayscale imaging while removing the reflective influence of a display or other nearby object.

The aspects and features described in connection with a certain of the previous examples can also be combined with one or more of the further examples in order to replace an identical or similar feature of this further example or to additionally introduce the feature into the further example .

It is further understood that disclosure of a plurality of steps, processes, operations, or functions disclosed in the specification or claims should not be construed to imply that those operations necessarily depend on the order described, unless explicitly stated in a particular case specified or is absolutely necessary for technical reasons. Therefore, the foregoing description is not intended to limit the performance of any number of steps or functions to any particular order. Furthermore, in other examples, a single step, function, process, or operation may include and/or be broken into multiple sub-steps, functions, processes, or operations.

If some aspects have been described in connection with a device or a system, these aspects are also to be understood as a description of the corresponding method. For example, a block, device, or a functional aspect of the device or the system corresponds to a feature, such as a method step, of the corresponding method. Accordingly, aspects described in connection with a method are also to be understood as a description of a corresponding block, element, property or functional feature of a corresponding device or system.

The following claims are hereby incorporated into the Detailed Description, where each claim can stand on its own as a separate example. Furthermore, it should be noted that although a dependent claim in the claims refers to a particular combination with one or more other claims, other examples may also include a combination of the dependent claim with the subject-matter of any other dependent or independent claim. Such combinations are hereby explicitly proposed, unless it is stated in individual cases that a specific combination is not intended. Furthermore, features of a claim are also intended to be included for any other independent claim, even if that claim is not directly defined as dependent on that other independent claim.

Claims (15)

A method (100) for determining an intensity value representing an intensity of light reflected from an object in a scene, the method (100) comprising: Performing (102) a time-of-flight, ToF, measurement of the scene using a ToF sensor, wherein a light intensity-independent correlation function of a photosensitive pixel of the ToF sensor has a plateau in a target measurement range for the ToF measurement, the object being within the Target measurement range is located, and determining (104) the intensity value based on an output of the photosensitive pixel for the ToF measurement. The method (100) according to claim 1 , wherein the light-intensity-independent correlation function indicates the distance-dependent correlation of the light of the photosensitive pixel with a reference signal and without considering the intensity of the light, the photosensitive pixel being driven based on the reference signal. The method (100) according to claim 1 or claim 2 , wherein determining (104) the intensity value comprises applying at least one correction to the output of the photosensitive pixel for the ToF measurement. The method (100) according to any one of the preceding claims, wherein performing (102) the ToF measurement comprises: illuminating the scene with modulated light; and driving the photosensitive pixel based on a reference signal, wherein the reference signal comprises an alternating train of high and low pulses of equal duration, and wherein the modulated light comprises a sequence of light pulses with the same pulse length and the same pulse spacing. The method (100) according to claim 4 , wherein a duty cycle of the modulated light is smaller than a duty cycle of the reference signal. The method (100) according to claim 4 or claim 5 , wherein the method (100) further comprises performing a further ToF measurement, wherein the reference signal used to drive the photosensitive pixel in the further ToF measurement is related to the reference signal used to drive the photosensitive pixel in the ToF measurement is used, is inverted, and wherein the intensity value is determined based on a difference between the output of the photosensitive pixel for the ToF measurement and an output of the photosensitive pixel for the further ToF measurement. The method (100) according to any one of Claims 4 until 6 , wherein the photosensitive pixel selectively stores charges generated in the photosensitive pixel during the ToF measurement in one of two charge storage devices of the photosensitive pixel depending on a signal value of the reference signal, and wherein the output of the photosensitive pixel for the ToF measurement based only on the charges accumulated in one of the two charge stores during the ToF measurement. The method (100) according to any one of Claims 4 until 6 , wherein the photosensitive pixel selectively stores charges generated in the photosensitive pixel during the ToF measurement in one of two charge storage devices of the photosensitive pixel depending on a signal value of the reference signal, and wherein the output of the photosensitive pixel for the ToF measurement based on a difference between the charges accumulated in the two charge stores during the ToF measurement. The method (100) according to any one of the preceding claims, wherein the light-intensity-independent correlation function has at least one further plateau in at least one further target measurement range for the ToF measurement. The method (100) according to any one of the preceding claims, further comprising: performing a further ToF measurement of the scene using the ToF sensor, wherein the light intensity-independent correlation function of the photosensitive pixel for the further ToF measurement has a plateau in a different target measurement area; and determining the intensity value based on the output of the photosensitive pixel for the ToF measurement and an output of the photosensitive pixel for the other ToF measurement. The method (100) of any preceding claim, wherein an absolute value of the light intensity independent correlation function at a predetermined distance is less than 10% of an absolute value of the light intensity independent correlation function at the plateau. The method (100) according to claim 11 , wherein a member covering the ToF sensor is arranged at the predetermined distance with respect to the ToF sensor. The method (100) according to any one of the preceding claims, further comprising: performing one or more further ToF measurements using the ToF sensor; determining a distance value indicative of a distance to the object based on an output of the ToF sensor for the one or more further ToF measurements; and Determine the target measurement area based on the distance value. The method (100) according to any one of the preceding claims, further comprising: generating a grayscale image of the scene including the pixel representing the determined intensity value. A device (200) for determining an intensity value representing an intensity of light reflected from an object (201) in a scene, the device comprising: a runtime, ToF, sensor (210), which is designed to carry out a ToF measurement of the scene, wherein a light intensity-independent correlation function of a photosensitive pixel of the ToF sensor (210) has a plateau in a target measurement range for the ToF measurement, wherein the object is within the target measurement area; and a processing circuit (240) configured to determine the intensity value based on the output of the photosensitive pixel for the ToF measurement.

Images